Flow cytometry (FC) is an essential resource in modern biomedical research. Cytometry resources at Case Western Reserve University (CWRU) are limited to a Coulter Elite 6 parameter cytometer that will electronically sort to 15,000 events per second, but is limited by coincidence to approximately 6000 cells/s. This instrument 's in the Flow Cytometry Core of the NCI supported CWRU Comprehensive Cancer Center and is the only cell sorter shared resource at CWRU. The core currently supports the research efforts of more than 70 laboratories with -85% funded by NIH, DOE, or NSF grants. The supported research is diverse and the facility operates as a flexible core that strives to meet the needs of all users who access the core on a formal first-come-first serve basis. The Medical School has expanded its research base significantly and steadily since the early 1980s and currently ranks 13th in NIH funding for US Medical Schools with $142,335,793 funding in 1999, and is the major research institution in Northeast Ohio. The FC core plays a significant role in the research infrastructure. The Medical School and University Hospitals faculty increased significantly over the last 3 years and plans indicate continued growth over the next 3 years. This proposal seeks funds to purchase a multiparametric high speed sorter to enhance the research efforts of 30 major users and 37 intermediate or minor users. If funded, his instrument will be added to the core facility and provide the following: (1) upgraded flow cytometric /cell sorting technology that will support funded programs; (2) increased instrument capacity that will allow the Core to respond to increased numbers of faculty and NIH funded projects; (3) insurance against significant disruption of research efforts during breakdown or scheduled maintenance - especially important for experiments that take weeks of planning; (4) permit creation of BL3 level sorting capacity to respond to NIH funded AIDS projects.